Renal function studies in chronic hydronephrosis

Abstract

This study was undertaken to clarify the site and nature of altered nephron function in chronic hydronephrosis in an attempt to evaluate the mechanism of its inability to produce a concentrated urine which had frequently been documented. For this purpose, the following three clearance studies were made in 30 patients with chronic bilateral or unilateral hydronephrosis and 7 unilateral hydronephrotic dogs.1) GFR, minimal and maximal urine osmolarity, water and solute excretion were measured under high water diuresis and subsequent antidiuresis induced by the administration of ADH in 4 normal subjects, in 10 bilateral and 5 unilateral hydronephrotic patients.2) Measurement of the rate of tubular maximal reabsorption of glucose (TmG) in 5 bilateral and 6 unilateral hydronephrotic patients.3) Measurement of the rate of tubular maximal reabsorption of solute free water (TcmH2O) in 7 unilateral hydronephrotic dogs produced by incomplete ligation of one ureter for 28 to 50 days.In unilateral hydronephrosis, clearance studies were made on each kidney after catheterization of each ureter up to the renal pelvis, using the normal side as a control.The results revealed a marked reduction of maximal urine osmolarity associated with decreased GFR of variable degree; decreased TmG in accordance with a decrease of GFR; decreased TcmH2O with a simultaneous decrease of TcmH2O/GFR in hydronephrotic kidney compared with normal kidney. Minimal urine osmolarity of hydronerphrotic kidney was found to be similar to that of normal kidney in unilateral hydronephrosis, although minimal urine osmolarity produced by bilateral hydronephrosis was invariably higher than that of the control. Excretion fraction of filtered sodium (EFNa) was revealed consistently elevated in hydronephrotic kidney of unilateral hydronephrosis as well as in bilateral hydronephrosis, indicating the urinary loss of sodium during and after release of urinary obstruction in chronic hydronephrosis. Plotting the serial changes of ureacreatinine clearance ratio against U/P creatinine ratio during the transition from water diuresis to antidiuresis and subsequent return to diuretic condition, there obtained one circular figure in normal kidney as illustrated by Thomas (1964), while such a figure was not observed in hydronephrotic kidney.These observations suggest that the basic integrity of the concentrating mechanism is not preserved with the intrinsic defect of sodium reabsorption at the distal portion of the surviving nephron of hydronephrotic kidney and the site involved may exsist in the renal medullary counter-current mechanism.